Physical exercise and skin microcirculation

One of the main role of skin is its involvement in thermoregulation. Skin blood flow (SkBF) is subject to great variations, depending on the environmental and body thermal status. Physical exercise imposes heat stress for the body and thus skin microcirculation. To achieve thermal homeostasis, SkBF and sweating are increased in response to exercise. The thermoregulatory response of SkBF during exercise differs from that at rest in the threshold for vasodilation and the sensitivity of the “SkBF-to-core temperature slope”. The purpose of this review is to highlight the response of skin microcirculation to physical exercise

Endothelium at a Glance

Exposed to the blood milieu and variable hemodynamic forces, endothelial cells of different vessels exhibit significant heterogeneity, directing also the variety of endothelial functions. Endothelial cells are actively involved in many physiological processes, including vascular tone regulation, fluid filtration and reabsorption processes, maintenance of blood fluidity and proper hemostasis, leucocyte trafficking, tissue repair, and angiogenesis; accordingly, healthy endothelium is crucial for vascular homeostasis. On the other hand, many exo- and endogenous harmful factors can cause endothelial dysfunction, associated with inflammation, thrombosis, pathological vascular wall remodeling, and predisposing to the development of cardiovascular and other diseases. In order to design accurate clinical and pharmacological strategies to postpone or ameliorate endothelial dysfunction, endothelial dysfunction should firstly be recognized. Therefore, understanding endothelial physiology is crucial for clinical measures to be timely taken. The review briefly outlines some basic concepts of endothelial structure and function, focusing on endothelial barrier function and endothelium-dependent vasodilation, and addressing some potential therapeutic targets. Additional specific concepts of endothelial (dys)function, with particular emphasis on its involvement in inflammation, hemostasis, and its (mal)adaptation to environmental challenges are extensively described in the following book chapters

The Physiology of Thermoregulation in Exercise: A Brief Review

During physical exercise, the production of heat in the working skeletal muscles increases, imposing heat stress on the body. Thermoregulatory mechanisms induce adjustments of cutaneous vascular conductance and thus skin blood flow (SkBF), sweating rate, and increased cardiac output to achieve thermal homeostasis. The response depends on the intensity, type, duration of exercise, and environmental temperature: during extreme exercise in a hot environment SkBF can attain up to 7 L/min compared to 300 mL/min at rest whereas the sweating rate can reach as high as 4 L/h. Due to opposing non-thermal reflexes, the thermoregulatory response of SkBF during exercise differs from that at rest: the threshold to induce vasodilation in the skin is shifted to higher body core temperature and the sensitivity of the “SkBF to-core temperature” slope is altered. Regular training induces better adaptations to physical stress which enable sportsmen to eliminate additional heat more optimally. The review emphasizes physiological mechanisms involved in thermoregulation during exercise and exposes some thoughts regarding the estimation t of the core temperature in humans, as well as some new approaches for an up-to-date assessment of parameters important for appropriate heat dissipation thereby maintaining core temperature

Power losses in synchronous reluctance motors

V članku smo najprej predstavili osnovne lastnosti, zgradbo in delovanje sinhronskega reluktančnega motorja, nato pa v okviru dvoosne teorije zapisali vezni model obravnavanega električnega stroja. Reluktančni navor omogoča vrtenje rotorja v sinhronizmu z glavnim vrtilnim poljem. Pri takšnem načinu delovanja (sinhronsko vrtenje) je v rotorju gostota magnetnega pretoka vedno enosmerna, kar narekuje brezizguben rotor. Vendar imamo zaradi statorskih utorov spremembo magnetne upornosti zračne reže, kar pri vrtenju povzroči utorske pulzacije magnetnega polja in s tem površinske izgube na rotorju. Na podlagi temeljnih elektromagnetnih zakonitosti smo izpeljali enačbo in z njo ovrednotili površinske izgube na rotorju motorja. Z obremenilnim preizkusom in preskusom prostega teka smo analizirali obratovalne karakteristike in izgube motorja. Kot posledico izgub smo nastalo temperaturno polje v motorju in na njem prikazali v obliki temperaturne slike.The aim of this paper is to present power losses in synchronous reluctance motors (SRM). Generally speaking, this type of motors is an unexcited synchronous machine with stator windings and a stator similar to any regular induction machine. The rotor is cross-laminated and contains flux barriers placed equidistantly around the air gap (Fig. 1). They serve to diminish the quadrature (q-axis) flux flowing between poles and at the same time they permit the direct axis flux to flow largely unimpeded through the poles. On the basis of the Parkćs theory, an impedance model of SRM for stationary operating modes is presented in a matrix form (Eq. 1). Further, the paper devotes special attention to surface power losses. The main flux of synchronous reluctance motors rotates at the same speed as the rotor. The presence of the stator openings gives rise to permeance variations causing a ripple in the main flux (Fig. 2) through which the rotor is driven and resulting in induced losses on the rotor surface. The same is going on on the stator surface due to the permeance variations in the rotor slot opening range. At normal tooth ripple frequencies, only eddy current components of these losses are of any significance and histeresis losses may be ignored. Eqs. (2-5) describe the magnetic flux density distribution and penetration into the rotor. Fundamental electromagnetic equtions (6-8) are used to calculate the eddy current distribution (Eq. 9) on a thin surface layer of a laminated rotor. Surface losses are calculated with Eq. 10 and presented in Figs. (3-4). The measured torque and current characteristics of SRM for asynchronous run are shown in Fig. 5. and for synchronous run in Fig. 7. The principle of the rotor load angle measurement is given in Fig. 6. No-load characteristics of SRM and power losses separation are presented in Fig. 8. Power losses at no-load operation of the measured prototype are separated and given in Table 1. To establish the surface losses impact on rotor temperature variations the temperature measurements (Fig. 9) were made. They are presentedin Table 2. Temperature variations for the SRM stator winding at a nominal load are given in Fig. 11

Wavelet analysis of laser Doppler microcirculatory signals: Current applications and limitations

Laser Doppler flowmetry (LDF) has long been considered a gold standard for non-invasive assessment of skin microvascular function. Due to the laser Doppler (LD) microcirculatory signal’s complex biological and physiological context, using spectral analysis is advisable to extract as many of the signal’s properties as feasible. Spectral analysis can be performed using either a classical Fourier transform (FT) technique, which has the disadvantage of not being able to localize a signal in time, or wavelet analysis (WA), which provides both the time and frequency localization of the inspected signal. So far, WA of LD microcirculatory signals has revealed five characteristic frequency intervals, ranging from 0.005 to 2 Hz, each of which being related to a specific physiological influence modulating skin microcirculatory response, providing for a more thorough analysis of the signals measured in healthy and diseased individuals. Even though WA is a valuable tool for analyzing and evaluating LDF-measured microcirculatory signals, limitations remain, resulting in a lack of analytical standardization. As a more accurate assessment of human skin microcirculation may better enhance the prognosis of diseases marked by microvascular dysfunction, searching for improvements to the WA method is crucial from the clinical point of view. Accordingly, we have summarized and discussed WA application and its limitations when evaluating LD microcirculatory signals, and presented insight into possible future improvements. We adopted a novel strategy when presenting the findings of recent studies using WA by focusing on frequency intervals to contrast the findings of the various studies undertaken thus far and highlight their disparities

Functional analysis of the bovine beta- and kappa casein gene promoters using homologous mammary gland derived cell line

Abstract. Bovine casein gene cluster belongs to the best studied regions of the bovine genome. However, molecular basis of the regulation of casein gene expression is still of great interest for the advancement of milk production. Identification of crucial regulatory regions governing casein gene expression would provide valuable information for marker assisted selection in dairy cattle. In our study we performed comparative analysis of the bovine beta- and kappa casein gene promoter sequences with the regulatory sequences from some other species. In addition, we used homologous mammary gland derived cell culture and luciferase reporter gene system to confirm the functionality of the proximal beta and kappa casein promoters. The longer kappa casein promoter (2064 bp) showed the highest expression level, followed by the short kappa casein promoter (925 bp) and beta casein promoter (1692 bp). Here we demonstrate the suitability of the bovine mammary gland derived cell line BME UV1 for transient gene expression under transcriptional control of the bovine casein gene promoters and compare functionality of different fragments of bovine beta- and kappa casein gene promoters using homologous in vitro system

Dietary Supplements and Sport Performance - A Comprehensive Review

Comprehensive articles on dietary supplements and their impact of on sport performance which would enable professional and recreational sportsmen evidence based information are sparse. Therefore, we investigated eight different dietary supplements, commonly used among recreative and endurance sportsmen according to available literature were analyzed, namely: Antioxidants, B-alanine, Branched chain amino acids (BCAAs), Caffeine, Carbohydrates, Creatine, Nitric oxide /nitrates, and proteins. Their mechanisms of action was shortly presented along with their potential beneficial and harmful side effects and safety. i.) Antioxidants: Sufficient amount of antioxidants is available in a balanced diet ii.) B-alanine: Supplementation is likely to be beneficial in high-intensity exercises. iii.) BCAAs: No review articles in English were available iv.) Caffeine: Caffeine supplementation is beneficial in endurance exercises v.) Carbohydrates: Carbohydrate supplementation is probably beneficial in exercises of durations longer than one hour vi.) Creatine: Creatine supplementation is effective in high intensity, short-lasting exercises, while it does not seem to have any ergogenic effect in aerobic exercises. vii.) Nitric oxide/nitrates: Nitrate supplementation has a small but meaningful performance enhancing effect, most apparent in situations of insufficient perfusion (hypoxia…). viii.) Proteins: Protein supplementation, in combination with resistance exercise, most likely has beneficial effects on lean body mass and muscle strength. Studies on the long term safety of the above supplements are mostly lacking. Most of the revised dietary supplements, if used for intended exercise regime, provide some sort of sport performance enhancement. On the other hand, the studies about the safety of the long term supplementation are mostly lacking